Tire inflation methods, also known as on-board inflation methods and traction methods, are well known, as may be seen by reference to the following U.S. patent Nos.: U.S. Pat. Nos. 5,516,379; 5,313,995; 5,273,064; 5,253,687; 5,180,456; 5,179,981; 5,174,839; 5,121,774; 4,924,926; 4,922,946; 4,917,163; 4,893,664; 4,883,106; 4,883,105; 4,825,925; 4,782,879; 4,754,792; 4,724,879; 4,678,017; 4,640,331; and 4,619,303. The entire disclosures of each of these patents are incorporated herein.
Typically, such systems comprise a source of pressurized fluid, a circuit leading from the source of pressurized fluid to the tires of a vehicle and a means to control the amount of fluid flowing from the source to the tires.
The prior art systems can be disadvantageous because often they have no means to prevent the highly pressurized fluid from the source reaching tires that do not need to be inflated. This can result in the incremental over inflation of tires that are already at their target or desired pressure. Over time, this can raise tire pressures close to the pressure of the source of fluid. Generally, over inflated tires are undesirable since they wear more quickly, they can change the ride characteristics of the vehicle and they are prone to failure. Tire failure can be catastrophic for a vehicle.
One example of a prior art system for inflating the tires of a vehicle is described in U.S. Patent Application Publication No. US 2005/0194080 which teaches a tire inflation system that provides short bursts of air of 0.033 to 0.065 seconds to a tire whose pressure is below a target inflation pressure. Once a burst of air is sent to the tire, a controller waits for a brief period of time for the system to stabilize. A delivery pressure transducer permits the controller to determine if the pressure reading is equal to or above the target inflation pressure after the burst is delivered. If the target inflation pressure has not been reached, the process is repeated with a larger burst of air. It is disclosed that the air supply source, which provides the burst of air, is kept at approximately 120 psi. It can be appreciated that providing larger and larger bursts of highly pressurized air can result in the over inflation of tires that do not need additional air since typically the under inflated tire or tires cannot accept all the air provided in such a high pressure burst.
U.S. Pat. No. 6,561,017 teaches a system that inflates a tire over a target pressure. The dynamic inflation is stopped and a static pressure is determined. If needed, short pulses of compressed air may be provided to close the gap between the static pressure and the target pressure. This patent also fails to disclose means to prevent the pulses of compressed air from reaching one or more tires that do not need to be inflated.